Tons of good beaches north of Cottonwood. Just go out and take your pick.
If you're ypu're looking for car access, there is an old airstrip directly across from Cottonwood on th AZ side. You can't launch from there, but it might work for a motorhome type deal if you don't mind a short climb.
Another option is the old Eldorado Marina site about 1/2 way between Cotonwood and Willow Beach on the NV side. There is still a road from Nelson down to the lake there and some good beaches too.
Mohave is a great place, especially the noth end. You'll have a great time.